Conventionally, in the fields where a roller bearing and other actuators are applied, such as a differential of an automobile and a transmission thereof, miniaturization and accomplishment of a high output are advancing. Hence, the environment of the usage of such an actuator tends to be a high-load condition and a high-temperature condition where the viscosity of a lubricant becomes low. Accordingly, the lubrication condition of the actuator like a bearing is changing to be more strict than ever, and a worn-out and a surface delamination due to improper lubrication become more likely to occur.
In order to improve such a lubrication condition, a technology is proposed which forms a lubricant puddle in a surface of at least either one of a rolling element and two components relatively moving, via the rolling element, to each other which is subjected to a relative rolling contact or sliding contact.
For example, Patent Document 1 discloses a technology of performing shot blasting on the flange face of an inner race to form concavities and convexities. Moreover, Patent Document 2 discloses a technology of forming a large number of minute recesses each formed of a concavity in the sliding surface of a sliding component by blasting with blast particles. Furthermore, Patent Document 3 discloses a technology of finishing the end surface or the flange face of a roller by a grindstone to form a finished surface including a gentle smoothed surface and recesses formed at random in the smoothed surface.
Still further, Patent Documents 4 to 6 disclose technologies of forming a large number of recesses of minute concavities at random in the rolling contact surface of a rolling element and the end surface thereof, the raceway surfaces of the inner and outer races and the large flange face of the inner race. According to those technologies, the lifetime of a roller bearing can be extended when the surface roughness parameter Ryni of the surface where the recesses are provided is set to be 0.4 to 1.0 μm, Rymax is set to be 0.4 to 1.0 μm, an Sk value indicating the distortion level of a roughness curvature is set to be equal to or smaller than −1.6, the ratio of recessed area is set to be 5 to 20%, and an average area is set to be 30 to 100 μm2.
Yet further, Patent Document 7 discloses a technology of causing a large number of recesses to be dispersingly present at random in a roller end surface, setting the arithmetic mean roughness Sa among the three-dimensional surface roughness parameters to be equal to or smaller than 0.1 μm, and setting the damping recess roughness Svk to be 0.15 to 0.30 μm, thereby improving the anti-seizing properties.